Yes its me again...Trying to make a simple cheap and effective non-return valve for multi-staging. came up with this idea (probably not original). Quick test on back lawn. Seems to work in principle. Nozzle is ejected out of bottles at end, but when staging there would be no pressure under so glue nozzle should stay in. A bit of Vaseline helps to keep it totally sealed. May not work under higher pressures....https://youtu.be/uuU4yL_lducJ

My thought is to build them pretty much like the diagram you had before as the increasing pressure pushes the valve closed tighter. I would laminate a few layers of fiber glass to build up the two sections (the guide and the seat). Get Blake to cut these to size for you, glue the guide in place, add your valve (I'd use a standard tap valve) and then glue the seat in place.

Gday Spaceman, Thanks for the reply. I'd rather not bother Blake (yet). i have made both valve systems but built the glue nozzle version for a test. It seems to work really well. If that fails, will go for the tap valve, which works ok except that stainless steel springs are expensive (even tiny ones!). Am looking for things to pull apart to find cheap ones. I did make it from off the shelf tubing and a piece of nylon rod and a hand drill. Not elegant... Note: I need to open a junk shop.Here's a very short video of where i'm up to on this build.https://youtu.be/Ttk-Dg_JYGsMore info on my blog which i just startedhttp://waterrocketsbrisbane.blogspot.co ... et-up.html

Nice video! Something to consider would be to ditch the non-return valve all together. If you just plug up the PVC pipe and make a small pin hole in it, it will still allow air to pressurise the upper stage but because the pressure difference is small when fully pressurised and with water surface tension you may find that very little water will leak back down to the lower stage. You can try that with just making a pin hole in a cap and half fill a bottle with water and then turn it upside down. You will get a little leakage initially but then it will stop because of the vaccum that forms at the top. If you are trying to optimize the water amount you can see how much water you lose before the water stops leaking and fill the lower stage that much less and add that much more to the upper stage so that when you stop pressurising you will have the right amount in each.

Once you launch, the pressure in the lower stage will drop and there will be a bigger pressure differential and water will start getting forced out of the tiny hole. However the amount of water loss will be very small by the time staging occurs.

The other big advantage of the small hole is that you can safely abort a launch remotely if the rocket is already pressurised. Something that's not straight forward if you have a non-return valve that seals well in the stager.

I also don't think the tube is necessary to emerge above the water line. That's useful for the clustered rockets but for staging a single nozzle you can save a little weight without it.

But I am very much looking forward to your flight report, the rocket looks great.